Semiconductor device

1. A semiconductor device comprising: a semiconductor substrate providing a drift layer having a first conductivity type; a base layer having a second conductivity type and arranged over the drift layer; a plurality of trenches that penetrates the base layer and reaches the drift layer; an emitter region having the first conductivity type, arranged in a surface portion of the base layer, and contacting the trench; an emitter electrode coupled with the base layer and the emitter region; a collector layer having the first conductivity type and arranged on the drift layer opposite to the base layer; a collector electrode coupled with the collector layer; a gate insulator film arranged over a wall surface of the trench; a gate electrode arranged in the trench via the gate insulator film, including a main gate electrode for providing an inversion layer coupling between the emitter electrode and the drift layer when applying a voltage thereon and at least one dummy gate electrode not contributing to generation of the inversion layer; a gate pad common to the main gate electrode and the dummy gate electrode; a first element that is arranged between the dummy gate electrode and the gate pad, shuts down or restricts conduction in order for the dummy gate electrode not to contribute to the generation of the inversion layer when a first voltage is applied to the main gate electrode via the gate pad in order to generate the inversion layer, and permits the conduction when a second voltage having a polarity reverse to the first voltage is applied to the gate pad; and a second element that is arranged between the emitter electrode and a connection point between the dummy gate electrode and the first element, permits the conduction when applying the first voltage, and shuts down or restricts the conduction when applying the second voltage.

2. The semiconductor device according to claim 1 , wherein: each of the first element and the second element is provided by a diode; and an anode of the first element is coupled with an anode of the second element.

3. The semiconductor device according to claim 1 , wherein: the at least one dummy gate electrode includes a plurality of dummy gate electrodes; and at least a part of the plurality of dummy gate electrodes is arranged above the collector layer.

4. The semiconductor device according to claim 1 , further comprising: a cathode layer having the first conductivity type, arranged on the drift layer opposite to the base layer, and arranged in parallel with the collector layer, wherein: the collector electrode is coupled with the collector layer and the cathode layer; the at least one dummy gate electrode includes a plurality of dummy gate electrodes; the semiconductor substrate includes an IGBT region functioning as an IGBT element and a diode region functioning as a diode element; the plurality of trenches are arranged in the IGBT region and the diode region; and at least a part of the plurality of dummy gate electrodes is arranged in the diode region.

5. A semiconductor device comprising: a semiconductor substrate providing a drift layer having a first conductivity type; a base layer having a second conductivity type and arranged over the drift layer; a plurality of trenches that penetrates the base layer and reaches the drift layer; an emitter region having the first conductivity type, arranged in a surface portion of the base layer, and contacting the trench; an emitter electrode coupled with the base layer and the emitter region; a collector layer having the first conductivity type and arranged on the drift layer opposite to the base layer; a collector electrode coupled with the collector layer; a gate insulator film arranged over a wall surface of the trench; a gate electrode arranged in the trench via the gate insulator film, including a main gate electrode for providing an inversion layer coupling between the emitter electrode and the drift layer when applying a voltage thereon and at least one dummy gate electrode not contributing to generation of the inversion layer; a main gate pad coupled with the main gate electrode; a dummy gate pad coupled with the dummy gate electrode; and a third element that is arranged between the emitter electrode and a connection point between the dummy gate electrode and the dummy gate pad, shuts down or restricts conduction when a predetermined voltage is applied to the dummy gate pad, and permits the conduction when the dummy gate pad is in an open state without applying a voltage thereon.

6. The semiconductor device according to claim 5 , wherein: the third element is provided by a resistor.

7. The semiconductor device according to claim 5 , wherein: the at least one dummy gate electrode includes a plurality of dummy gate electrodes; and at least a part of the plurality of dummy gate electrodes is arranged above the collector layer.

8. The semiconductor device according to claim 5 , further comprising: a cathode layer having the first conductivity type, arranged on the drift layer opposite to the base layer, and arranged in parallel with the collector layer, wherein: the collector electrode is coupled with the collector layer and the cathode layer; the at least one dummy gate electrode includes a plurality of dummy gate electrodes; the semiconductor substrate includes an IGBT region functioning as an IGBT element and a diode region functioning as a diode element; the plurality of trenches are arranged in the IGBT region and the diode region; and at least a part of the plurality of dummy gate electrodes is arranged in the diode region.